Methods and/or devices described herein generally relate cardiac pacing therapy. More particularly, they concern methods and/or implantable stimulation devices for determining pacing pulses regimens in response to sensed and/or other information, particularly information indicative of tissue depolarization and/or arrhythmia.
A goal of cardiac pacing therapy is to xe2x80x9ccapturexe2x80x9d heart tissue, typically through administration of an electrical stimulus, e.g., a pacing pulse. Capture is achieved when an applied stimulus causes xe2x80x9cglobalxe2x80x9d depolarization of the heart""s myocardial tissue leading to contraction. The stimulation-capture process allows for therapeutic management of various cardiac functions. For example, abnormal heart tissue contractions, known as arrhythmias, which include bradycardia (slow heart rate), tachycardia (fast heart rate), any markedly irregular rhythm, blocks and/or the presence of premature contractions, are manageable through use of stimulation-capture therapies.
Arrhythmias are often problematic and interfere with a heart""s normal pumping function. In a normal heart, a pump cycle beings with a stimulus originating at the sinoatrial node, which then travels to intranodal atrial conduction tracts and the Bachmann""s bundle and causes the atria to contract and pump blood into the ventricles. The stimulus next travels to the atrioventricular node, the Bundle of His, and the Purkinje system where the stimulus causes simultaneous contraction of the right ventricle, which pumps deoxygenated blood to the lungs through the pulmonary artery, and the left ventricle, which pumps oxygenated blood to the body through the aorta, the body""s main artery. In an arrhythmic heart, the stimulation process is corrupt and capable of disabling the heart""s pumping action. Pacing therapy seeks to terminate or overcome arrhythmic processes and allow the heart to function normally.
A variety of methods and implantable devices exist for terminating arrhythmia and/or pacing heart contractions. For example, U.S. Pat. Nos. 6,081,764 (Pendekanti, et al.) and 6,085,116 (Pendekanti, et al.) disclose methods and implantable devices for atrial defibrillation and U.S. Pat. No. 6,154,672 (Pendekanti, et al.) discloses methods and implantable devices for ventricle defibrillation. The ""764, ""116 and ""672 patents are, for all purposes, incorporated herein by reference.
According to the ""764 and ""116 patents, a pacing pulse regimen is used to reduce the shock energy required to terminate atrial fibrillation or to even eliminate the need for a defibrillation shock (a cardioversion level stimulus). In this approach, the pacing pulse regimen constitutes a first treatment tier and the defibrillation shock constitutes a second treatment tier. The first tier pacing pulse regimen consists of a train of pulses delivered to one or more pacing sites in the atrium over a duration of approximately 1 second to 10 seconds. Throughout the duration of the pulse train, the pacing interval (time between successive pulses in the train) at any given pacing site is calculated as a percentage (e.g., preferably 80% to 95%) of the atrial fibrillation cycle length (AFCL), which is the time between successive atrial fibrillations. Thus, given an AFCL value on the order of 100 ms, a two second pulse train will deliver approximately 20 pulses. According to the ""764 and ""116 patents, the otherwise fixed pulse rate may be incremented after each pulse by a prescribed amount, which is not determined in real time.
These two patents also disclose increasing the pulse interval for verification of capture, or alternatively, decreasing the pulse interval if capture is not verified. However, the ""764 and ""116 patents do not disclose methods to determine, sense or verify capture. Furthermore, methods to increase or decrease the pulse interval in relation to capture are not disclosed.
The aforementioned ""672 patent discloses methods and devices for ventricular pacing therapy for terminating ventricular fibrillation. According to the ""672 patent, an equal-interval train of pulses is administered to ventricular tissue with a pulse interval based on the ventricular fibrillation cycle length (VFCL), which is the time between successive ventricular fibrillations. The ""672 patent discloses a two tier approach that applies a first tier pacing pulse train to reduce the energy required by a second tier ventricular defibrillation shock. The ""672 patent does not disclose sensing or detection of ventricular depolarization in response to pulsing. Instead, only VFCL is detected, which is subsequently used to modify the pacing therapy.
Accordingly, there is a need for pacing therapy that determines pacing pulse regimens and/or whether to administer cardioversion level stimuli on the basis of information indicative of tissue depolarization, in particular, regional or local depolarization.
An implantable cardiac stimulation device is programmed to administer pacing therapy based, at least in part, on information indicative of tissue depolarization. In essence, information indicative of tissue depolarization may allow one to assess the effectiveness of a stimulation pulse administered to the heart. In one implementation, a pacing pulse is administered to heart tissue. Next, a sensor obtains information indicative of tissue depolarization related to the administered pulse. This pulse-sense cycle is optionally repeated and the information analyzed to determine whether parameters for a subsequent pacing pulse (or pulses) should be altered, or alternatively, whether a cardioversion level stimulus should be delivered.
This approach, as discussed herein, extends beyond that contemplated by traditional pacing therapies in that information indicative of depolarization, in particular regional or local depolarization, is obtained and analyzed in real time, for example, during a pacing pulse regimen. As described herein, regional and local refer to tissue proximate to a stimulus electrode or electrodes. Various methods described herein optionally aim to depolarize tissue in a controllable and coherent manner. Information germane to depolarization is useful to determine and/or modify a pacing pulse regimen in real time, as well as, to determine whether a cardioversion level stimulus should be administered. The methods and devices disclosed herein are further optionally useful in applications that use multiple sense and/or stimulation electrodes in one or more chambers of the heart.